Ion channels are transmembrane proteins that participate in distinct physiological and pathophysiological processes. Generation of transmembrane potentials, signal transduction, excitation-contraction (or secretion) coupling in different cells are essential biomedical phenomena in which ion channels play decisive roles. Ion channels are extremely complex membrane proteins. This complexity is a major challenge for the proper understanding of molecular structure-function relationships of ion channels in cell membranes. The long-range goal of this application is to understand how the structure of a simple ion channel relates to its function. The specific aims are: 1) to synthesize different dioxolane-linked gramicidin A ion channels. The structural difference between these channels, which are gramicidin A (Ga) dimers, is in the polarity of different chemical groups attached to the dioxolane linker (middle of the channel. 2) To perform different and thorough computational models of different ion channels. This information will be used to supplement and understand the biophysical properties of our different ion channels in lipid bilayers. The aim is to understand how structural elements of molecules respond for a given functional behavior. 3) The biophysical properties of proton currents in different dioxolane-linked dimers will be studied. Gating, permeation, test of a specific hypothesis concerning proton jumps at the membrane-solution interface, kinetic isotopic and temperature effects will be evaluated in different dimer channels, and in different lipid bilayers. In particular, the mechanisms by which methanol attenuates proton currents will be explored in detail. Effects of different structures of the same or different ion channels on gating and permeation of Na, Cs and K will also be studied. An essential part of this application is the study of proton movements in different dioxolane-linked gA channels. In spite of its central role in the origin and maintenance of life (ATP generation), the molecular mechanisms by which protons are transferred across biological structures are not known. Some human diseases are directly or indirectly linked to the malfunctioning of ion channels. The precise relationship between structure and function of ion channels is not known. The understanding of basic mechanisms by which ion channels work represents an essential step in identifying the precise molecular cause of a disease. This has the serious potential of contributing to the development of therapies that will cure or control the pathological process underlying the disease. The experimental results that will be obtained in this project will certainly be of learning value to understand how ion channels work.